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So tis the season for the usual car runs rough on start up, misfires, CEL/MIL, stalling. Before you get too deep into this thread, I believe most of the data is relevant to the 325/330 models, or typical the 2.5L M52tu and 3.0L M54 engines also used in the E39 5 series and E85??Z4 series (however, it may be relevant to the 323/328 models as well, but part numbers will probably vary?), please check part number and application carefully before placing parts orders.

First suggestion to help you move in the proper direction is get your CEL/MIL codes read. Start a log and note the date, mileage and each trouble code. If there are freeze frame codes, note these as well. Then clear your codes, NOTE YOU WILL NEED AN ODBII SCAN TOOL TO CLEAR YOUR CODES, also NOTE IF YOU ARE NOT USING A BMW SPECIFIC SCAN TOOL (PEAKE, GT1, PA SOFT, CARSOFT, ETC.) YOU MAY ONLY GET A PARTIAL PICTURE OF WHAT CODES YOUR CAR MAY HAVE. The idea here is each time your CEL/MIL lights up, try to read, log and and clear your codes ASAP. This will help you identify what code(s) show up first and will help you narrow your problem before other codes show up and may mislead you.

If you do not have a code reader or scan tool, many auto parts stores (Auto Zone, Advance, Pep Boys, O'Rielly, Fisher, etc.) will allow you to borrow one and usually use it in their parking lot. Even if it does not support BMW specific codes, most of the problems I have documented fall within the generic OBDII powertrain error code group. Codes usually are in the format of Pxxxx, example P0174. Please note that the bulk of this thread has to do with problems on cold start up and during idle situations. There have been a number of cases lately where codes P0171/P0174 are not triggered at idle, but at highway cruise speeds. I suggest you cover the bases with the very common solutions listed below, but if once you have cleared the obvious problems and if you are getting P0171/P0174 at highway cruise speeds only, then you are most likely not dealing with a standard intake or crankcase vacuum/air leak. I will be adding information to this thread in the near future for lean codes at highway cruise speeds

IMPORTANT INFORMATION

As mentioned above, the bulk of this thread has to do with idle based problems, usually caused by vacuum/air leaks, but we have started to see a few cars that owners have addressed all the obvious vacuum/air leaks and they are still getting mostly Lean codes, many times without DME misfire codes. In a number of these instances the problems only show up during highway cruising situations, the CEL will not trigger during start up or any in town sub 45 MPH driving. But once the car is brought up to highway cruise type speeds, a few cars are still triggering the CEL along with P0171 & P0174. In many of these cases the problem has been with soft failed MAF's that are under reporting the amount of intake air, therefore causing the mixtures to be adjusted lean, then triggering Lean P0171 & P0174. So in some cases you may have a soft failure on a MAF where the engine is misfiring and running poorly and/or in a limp mode without any specific CEL or DME trouble codes.

Some cases we have seen soft failures on fuel pumps and/or fuel filters that either the pressure regulators are not working correctly and possibly issues with the fuel pressure regulator vacuum hose, even restricted fuel filters with 80-120k miles of fuel passing through them. Some of the soft fail fuel pump failures are causing P0171/P0174 without misfire and may only happen off idle when cruising. Sometimes even causing idle surge and instability without triggering the CEL or codes. Please cover the basics and take care of simple things like spark plugs, fuel filter and fuel pressure regulator vacuum hoses before spending a lot of money on other parts.If you do not know the history on your spark plugs and fuel filter, it is probably time to change them!

FUEL PUMP ISSUES

This is not really part of the simple vacuum leak/hose problems that were originally outlined, but BEWARE there are soft failures on fuel pumps that can lead to intermittent hesitation, rough idle, misfires and stalling.

A PM replacement of the pump, fuel filter and fuel pump relay may be a good idea. Parts cost if you do your homework should be under $200 and take about 1 hour. The best pump prices are from www.bmaparts.com from what we have seen lately. Fuel filter pricing on Amazon is pretty good as well.

Other items to possibly consider, but may not have been identified as actual causes of lean codes are as follows: camshaft timing may be out of spec possibly due to prior cylinder head removal and/or timing chain work, VANOS seals possibly casing camshaft timing to be off, throttle body/TPS issues. These are things to consider and to look into, many of these issues have not been proven to be a cause of the lean codes, however, just additional items to think about. Also keep in mind that pre Cat O2 sensor health is also important for proper reporting of fuel mixtures. And the last thing to think about is engine to body grounding. If for some reason the ground path between the engine and body/DME is questionable, you again may have incorrect reporting of sensor date, therefore possibly causing problems with CEL and DME trouble codes. So look at the charging Voltages and check the engine to body grounds while under the hood. Camshaft position sensors are also known weak points in these cars and they can also soft fail causing incorrect camshaft position feedback, thereby causing the VANOS to not work properly and possibly impact performance enough to cause Lean codes to be triggered.

But in any event, I would start with reading the DME trouble codes and uses these as clues, check all the obvious source so vacuum leaks, replace known problem hoses, gaskets and intake boots, then see where this all leads you. Additionally many maintenance related items should also be addressed before jumping into more costly and difficult sensor replacement.

Most of the problems I mention in this thread trigger one or more of the follow codes, but not limited just to these codes:

Below are some of the MOST common problems/solutions. There may be other things that cause similar problems, but these are fairly easy to check visually, cheap and easy repairs. Many owners tend to just want to have a high priced single solutions like MAF, O2 sensors, ICV, Coils, Fuel Pumps, keep in mind that some of these items may be a contributing factor, however, it does not matter how many $100-$200 parts you throw on the car, if you have rubber hoses and gaskets leaking air, all the hard parts in the world will not solve your problems, they may help, but why not check the simple and cheaper things first, then check them off your list before you move forward. Except for the DISA O-ring, most of the other things can be visually inspected and tested very simply without a lot of dis-assembly. You can then rule these items in or out as potential problems within a few minutes if you know exactly what to look for.

Many of these problems are due to intake air leaks and/or crankcase air leaks of some sort, usually due to loose, damaged, broken or deteriorated parts, most likely rubber or plastic. Do not rule out crankcase leaks as the design of the engine keeps the crankcase under a small vacuum most of the time. A crankcase air leak is basically an intake air leak in these cars. The problem could be as simple as a dipstick not fully seated, a bad or loose oil fill car or a bad valve cover gasket or cracked valve cover that does not leak oil but can leak air/vacuum. Also in more extreme cases you can have vacuum leaks at the intake manifold to cylinder head connection. These gaskets have silicon rubber seals that can get heat set in the compressed state and leak only on cold start up situations.

A few ways to find and locate vacuum/air leaks is with a smoke tester (Internet search for more on smoke testers), using additional vacuum hose and using smoke inhaled from a cigarette or cigar, then blowing it into the vacuum hose to fill the intake or other vacuum lines, using a mechanics stethoscope with the transducer removed so you have open hose to you ears to attempt to locate a vacuum leak source while the engine is running, a 4 foot piece of hose to hold up to your ear to listen for vacuum leaks when the engine is running, and last but not least is a can of spray brake cleaner to spray and pinpoint vacuum leaks while the the engine is running. The spray brake cleaner will cause the engine RPM to increase slightly and smooth out when a leak is pinpointed. I have found via experience that very small and hard to find vacuum leaks, like where an intake manifold meets the cylinder head can be found much easily with spray brake cleaner than smoke testing or other methods. Also a note on smoke testing, many people swear by these, however, in practical terms, the smoke tester usually operate on very low pressure, usually 2-5 psi, they are usually only good for locating very obvious leaks that you should be able to find with visual inspection if you know where to look. I find that smoke testing may not show very difficult leaks like silicon gasketed surfaces such as the DISA or intake to cylinder head mating surfaces, this is where sometimes spray brake cleaner works much better. Be careful with spray brake cleaner on painted surfaces, breathing the fumes too much or getting it in your eyes due to splash back or air flow off the engine cooling fan. Use your head and be safe while working under the hood with the engine running, watch out for moving and hot parts, be aware of high Voltage ignition components and spraying flammable chemicals around!

Not in any specific order, but if you own an E46 (Actually almost any 6 cylinder BMW prior to the cut over to the e9x series models in 2005/2006), they are old enough now that these items should be replaced soon anyway. Please verify correct part numbers @ www.realoem.com to make sure you purchase and have the correct part numbers for your vehicle repair.

1. DISA Valve (sometimes referred to as an Adjuster Unit) #7 in this link - http://realoem.com/bmw/showparts.do?...79&hg=11&fg=40. The DISA has a number of different failure modes, the DISA can have problems anywhere from vacuum leaks to catastrophic failure that may leave butterfly floating loose in the intake plenum and possibly the rear metal pivot pin could fall out and be sucked into once of the cylinders causing pretty severe engine damage.

SPECIAL NOTE ON THE REAR DISA PIN - The rear DISA pin can and will fall out depending on how badly the DISA butterfly plate is worn on the actuator shaft. This metal pin appears to be pressed into the rear of the butterfly and rotates with the butterfly plate. If the butterfly has become cracked or is overly loose on the actuator shaft, this metal pin (about 1/4" in diameter and about 13/16" long) could possibly become loose, fall out of the DISA assembly and work its way into a cylinder and may possibly cause severe engine damage. If you remove the DISA, immediately look for the rear metal butterfly pin and make sure it is still firmly pressed in. If you do not find the pin, check the intake VERY carefully for the pin and remove it if you find it. If you find the pin and it is loose in anyway, please remove the DISA flap and rear metal pin if you need to reinstall the existing, worn out DISA until you can purchase and install a new DISA

The first thing you want do is remove the DISA valve, pretty easy overall, remove the intake air filter box, upper intake boot and a few wire connectors and you are ready to access the DISA, you will need the Torx bit to actually remove the 2 DISA mounting screws. Once the DISA screws are removed, ease the DISA out of the intake, do not force it, there is only 1 angle that the DISA will likely come out and go back into the intake, it is not hard once you find the proper angle.

If the DISA valve slides out of the intake the first 1/4" easy, without much effort, or almost falls out, you will need a new O-ring!

Now that you have the DISA out of the intake, you need to check other functions to make sure you even want to re-use the DISA long term.

Special note for inspecting DISA valve, while you have the DISA out, inspect the DISA for proper operation. The DISA butterfly should be spring loaded in the open position and the butteryfly should not be overly loose or sloppy in the DISA shaft. You can also shake the DISA and it should not be noisy (new DISA will make absolutely no noise or rattle if shaken VERY hard). If you have any noise when shaking the DISA, something is most like worn and/or broken and you should consider a replacement DISA. Also the DISA rear pin can fall out into the engine and the DISA butterfly valve can fall off and get stuck in the intake possibly blocking the airflow to 1 or more cylinders, so it you remove the DISA and see no butterfly flap or rear metal pin, get worried and start looking for spare parts in the intake. If you are lucky the rear metal pin will be in the DISA groove in the intake.

Keep this in mind in case you suspect your car may have already had a replacement DISA, and if you have some strange performance issues, maybe someone left the old butterfly in the intake manifold if it fell off the original DISA??

The DISA is vacuum controlled and the small vacuum actuator on the end of the DISA is what actually moves the butterfly valve along with a control solenoid. Overall the DISA is a very ingenious device. The large body is actually vacuum reservoir. If look closely there is a very small hole near the butterfly valve this is the actual vacuum source. To verify if the vacuum actuator is still working and not leaking, close the DISA butterfly with your hand and then put your thumb over the opening that is opposite side of the electric connector on the solenoid. What should happen is the DISA butterfly will spring back open about 1/4" beyond the DISA frame. If the butterfly pops all the way back to the open position or slowly moves back to the default open position, then the vacuum actuator diaphragm is leaking and the DISA will not function correctly.

While there may be some sources that offer DISA "rebuild" kits, I would stay away from them personally. The butterfly valve and shaft are only part of the DISA, there is also an electrically controlled solenoid, actuator shaft seal and a vacuum diaphragm that actually moves the DISA valve and these parts can and will fail. The shaft/butterfly failure usually happens sometimes after the 100k mile mark, so if you car has the original DISA still, it is most likely ready for a replacement by now anyway. The vacuum diaphragm is more likely to fail than the solenoid and if the vacuum diaphragm fails you will end up with ANOTHER hard to find vacuum leak. There have also been a few reports of DISA vacuum actuators that test fine before the DISA repair kit was installed, but after removing the shaft and butterfly valve, after the vacuum actuator link was tweaked and twisted, the vacuum diaphragm was then cracked and no longer properly held vacuum. This is kind of expected from a decade old flexible rubber diaphragm, so just beware and be forewarned. If you are reading this thread, your car is clearly old enough now that if the butterfly is loose on the shaft or the DISA rattles when you shake it, just do yourself a favor and buy a new DISA and be done with your problem DISA for the next 7-10 years.

If you feel the DISA is physically in good shape and the vacuum diaphragm for the actuator is still in good shape and holds vacuum, then you may just need to replace the primary O-ring, which is not typically serviceable, however, you can get a red silicon replacement on for under $12 online or someone mentioned you might be able to match up something at your local parts store. Recommend a silicon O-ring as it is a bit softer than some of the harder rubber compounds and will tend to seal better with the plastic expansion and contraction over wide temperatures. I would be so inclined to put this replacement on a new DISA anyway as the DISA seal is only good for about 5 years/50k miles, after than you are on borrowed time. If for some reason you remove the DISA to replace the lower intake boot or do other work on the car, REPLACE the O-ring or you will be sorry once it gets below 40F. Trust me.

If you think your DISA should be replaced, following are some of the most common part number, but please check the part number before ordering a replacement for your vehicle. DISA prices online are between $175-$225 depending on the part number and the supplier. Prices change, however, check www.bmwmercedesparts.com for pricing as if this entry they have the 3.0 L DISA for $176.

DISA BMW part number - Please verify these via www.realoem.com to confirm proper application.
325/2.5L engines appear to use BMW Part #11617544806, this appears to have superseded an earlier BMW Part #11617502269
330/3.0L engines appear to use BMW Part #11617544805, this appears to have superseded an earlier BMW Part #11617502275
Both of the 325/330 DISA's have the injected or mold orange silicon main seal. SPECIAL NOTE - The 325 and 330 DISA appear to be very close in size, the main intake hole opening is the same size, however, the 325 DISA will fit into a 330 intake opening, but not the other way around. The 330 DISA is about 1/2" longer overall. Make sure you did not or do not end up with the 325 DISA in a 330 intake. I believe the 330 DISA will bottom out in the 325 intake before the flange meets the intake surface. As a point of reference, the last 7 digits of the DISA part number will be cast into the side of the DISA next to a BMW logo. So a 325 DISA should have either 7502269 for the original part up through 4/04 or 7544806 for the newer version used after 4/04. The 330/3.0L DISA should have either 7502275 for the original part up through 4/04 or 7544805 for the newer version used after 4/04.

323/328 2.3L & 2.8L engines use DISA BMW part number - 11611440049, with the green removable O-ring. I have not confirmed for sure that the 2.3L/2.8L DISA has the part number cast into the side, but if it did, I assume it would have 1440049 after the BMW logo on the side of the DISA? Please verify part number and application.

If you feel your DISA is still serviceable, then I definitely suggest replacing the primary O-ring. Again, please measure your DISA and/or make sure when you order a replacement O-ring to specify your engine model as there are differences between the 323/328 & 325/330 series engines.

Note about the O-ring replacement, the 325/330 DISA has an orange molded/injected silicon seal in the groove, the 323/328 engines have a standard replaceable green O-ring. On the 325/330 you need to take a small screw driver and maybe a brass wire brush to scrape the groove clear of the original silicon before installing the new replacement O-ring. Then lube the O-ring with some silicon spray or clean light oil before reinstalling the DISA. The DISA will take some effort to seat it the last 1/4".

I do not suggest using any sort of sealer on the DISA O-ring area. There is an issue where the material needs to expand and contract to seal over temperature and any sort of sealer will not really work for the type of interface where this needs to seal in the inside of the hole in the intake manifold. What will happen is any sort of sealer will likely just make a mess that will need to be cleaned up once a proper O-ring has been installed.

PLEASE MAKE SURE YOU HAVE CLEARLY READ THE DISA SPECIAL NOTE ABOVE ABOUT THE REAR METAL BUTTERFLY PIN, WARNING, THIS PIN CAN FALL OUT ON EXTREMELY WORN DISA'S AND POTENTIAL CAUSE SEVERE ENGINE DAMAGE IF SUCKED INTO A CYLINDER

Your local auto parts suppliers may have something that fits?? Examples - Auto Zone, Advance, Pep Boys, O'Rielly, Fisher, but this may be a wild goose chase and it would probably be better to order the O-ring online so you will get something a bit closer in fit.

For the 325/330 M54 engines, the DISA O-ring is not a serviceable part, you have to remove the orange injected/molded silicon sealer and clean the groove out and install a replacement O-ring.

DISA O-rings for the 323/328 engines have the following dimensions.This is for DISA's with the green, removable O-ring, not the orange molded seal. I also believe that the green O-ring DISA's are less problematic than the DISA's with the orange molded seal?

2. Lower Intake Boot, #6 in the this link - http://realoem.com/bmw/showparts.do?...05&hg=13&fg=15, cracked or torn, usually at the small elbow connection point due to stress on the boot and the high under hood temperatures. About $20 depending on where you purchase it. Note that to really get at this, it is easier to take the DISA valve out to give you better access. Look very closely at the small flexible tube on the lower elbow as this is usually where the cracks occur. Its almost like you should just replace it anyway if it appears original as the rubber gets hard and cracks. A few notes, the hose clamps on the lower boot are very hard to reach. Many people cut the old boot to gain better access to the hose clamps. A 1/4" drive socket set with flex ratchet and a very long flat blade screw driver (12+") help here. Once hose clamp is loose, rotate then try to use the long screw driver to finish loosening the clamps. Also if you plan on replacing the upper intake boot, cut a slit along the plastic F connector so you do not break the connector trying to remove it from the original upper boot. Use silicon spray when installing the F fitting into the new upper boot.

The parts numbers below are known to be for 325/330 engines, but again before you order parts for your car, please visit www.realoem.com and verify the proper part numbers for your application.

Lower boot, BMW part number - 13541435627 , this is the most common failed boot
Upper boot, BMW part number - 13541705209
F vacuum fitting, BMW part number - 13327503677

3. CCV (Crank Case Vent) lower oil drain hose, #4 in this link - http://realoem.com/bmw/showparts.do?...94&hg=11&fg=15, BMW Part #11157532649 or for cold climate BMW Part #11157532629 which is probably the best option for all cars, it just has more insulation to keep it from freezing as easily if there is a lot of condensation in the oil. Also on Amazon - http://www.amazon.com/11157532649-98...7346039&sr=1-2
Connects between the dipstick tube and the bottom of the CCV. The connection to the bottom of the CCV is a bit tricky to unlatch blind, but it can be performed without taking anything but the air filter box out. I find if you get the end of the hose off the dipstick it makes it easier to rotate the snap fitting on the bottom of the CCV. I use a long (14-16") flat blade screw driver to help push off the CCV oil drain hose from the bottom of the CCV while I squeeze the release bail as it is VERY hard to squeeze the release bail and pull down at the same time from under the hood. It is not easy to get your hand down there, but it is possible. Make sure you hear a sharp click when you reinstall the oil drain hose, otherwise your bail connection is not secure.

There are other hoses connecting the CCV and they may also go bad over time, however, the lower oil drain hose seems to be the most common failure point. Additionally the CCV valve itself and the dipstick tube can also cause problems, however, these may be more to do with oil plugging the drain passages and cause oil leak and even possibly hydro lock the engine if things go really bad. More often in the much colder climates, however, the CCV is an issue all to itself and a search on the board here will offer many stories and solutions. One very good overall CCV thread is this one - http://forum.e46fanatics.com/showthread.php?t=870406

Pictures of a failed lower CCV oil drain/return hose are below. Note the thicker hose is the cold weather part number, this is what I would suggest installing. If you are in a bind, you can use 3/8" fuel line 10 3/8" in length but you may need to use spray silicon or heat the end of the hose to get it onto the CCV drain connector. It is a bit difficult to release the CCV hose connector in the blind, but if you notice it had an oval shape release collar, you pinch the wider part of the collar to make is circular and then it should release straight downward.

The parts numbers below are known to be for 325/330 engines, but again before you order parts for your car, please visit www.realoem.com and verify the proper part numbers for your application.

4. SAP (Secondary Air Pump) issues - First you need to make sure the SAP air pump actually runs. There are electrical controls, fuses, connectors that can contribute to a non working SAP air pump. Additionally the actual pump can fail as well, there are bearings that can and will go bad, causing a very noise pump and the bearings could possibly seize as well. I expect theh pump could also fail electrically, but for the most part I have seen/heard pumps with bad bearings that get extremely noisy. Noisy to the point that the pump can be heard 3-4 houses away when the car is started in the morning! So if you have any SAP specific codes, please make sure your SAP pump motor is working before you focus too much on hoses, valves and other items.

Rubber hose between the air pump output and the SAP air control valve, item #2 the following link for earlier cars - http://realoem.com/bmw/showparts.do?...88&hg=11&fg=50. There appears to be AT LEAST 2 different part numbers depending on the model and year of car, BMW Part #11727555680 appears to use hose clamps on earlier cars, BMW Part # 11727555681 appears it may have quick connects used on later cars or 3.0L engines (330 cars)?? Check the part number of your application on www.realoem.com.
Might not cause stalling or a misfire, but can cause a CEL/MIL to light. These hoses start to break down due to the high heat from the exhaust transferring to the SAP air control value. They can cause problems with the SAP air control valve clogging or getting blocked.

SAP air control valve vacuum lines, items #3 & #4 in this link (Note - not all cars have a vacuum operated SAP air valve)- http://realoem.com/bmw/showparts.do?...03&hg=11&fg=45 (both hard and soft line along the valve cover where the O2 sensor wires are routed) can leak vacuum and cause rough engine during cold start and possibly CEL as well. The SAP vacuum hoses, mainly the hard plastic pipe, crack due to heat over time and usually cannot be seen. Also the vacuum hose to the SAP air control valve usually do not pull vacuum except for the first 90 seconds on cold start so they often get missed when inspecting for leaking vacuum hoses. Note that not all engines have this SAP check value vacuum hose. I believe?? 3.0L engines/330 cars may not have this vacuum operated check valve (still trying to verify this)??? I believe if your air pump main output hose has the quick connect ends and not standard hose clamps, the SAP check valve is not vacuum controlled??

Also keep in mind there are a few other parts associated with this vacuum control circuit. There is the electric control solenoid valve, a vacuum check valve and a few other short vacuum hoses under the rear of the intake manifold and they are VERY hard to see and access, again, not all engines have this configuration. The electric check valve has been known to get debris in it from deteriorating vacuum lines and hoses. This debris can either block/clog the electric control solenoid valve or it may cause the debris to keep the electric valve from completely closing. If this electric valve gets partially stuck open I am not sure what symptoms will show up. The small plastic check valve and the few associated short vacuum lines can also be a problem. The issue is they are very hard to inspect and access. See picture of the underside of the intake manifold below a better view of what these items look like.

Simple test for the SAP air valve vacuum hose is to disconnect the small vacuum hose at the SAP air valve and connected a vacuum gauge to this connection and make sure there is vacuum applied for approximately 30 seconds or more on cold start up. The vacuum gauge should read approximately 15+ inches of vacuum. If you do not have a vacuum gauge, you should be able to use your finger to block the end of the hose to see of the hose is pulling vacuum on cold start up. If you do not get vacuum, then it is likely there is a problem with the vacuum hoses between the SAP air control valve and the connection under the rear of the intake manifold. Most likely cause is the hose and hardline from the SAP vacuum control solenoid under the intake around the rear of the valve cover and along the side of the valve cover near the O2 sensor wires.

The SAP vacuum control solenoid and a few additional shorts vacuum lines and a small check valve are all buried way underneath the rear of the intake manifold and are very hard to see and access. You really need a good light and a mirror. These short sections of vacuum hose and the small check valve can also be problems and you cannot easily tell if they are a problem, but I would probably replace the vacuum hose between the SAP air control valve and the SAP vacuum control solenoid first before I fought with the parts under the intake.

Note the vacuum line from the SAP vacuum control solenoid to the SAP air control valve only has vacuum applied for the first 30-120 seconds (typically around 90 seconds) on cold start up. So if you car runs fine from 90-120 seconds and beyond, I would think this is a likely source of your problem.Also keep in mind the SAP vacuum control solenoid vents to atmosphere when de-energized (engine off or SAP not running) , so you blow backwards from the SAP air control valve or use a smoke tester you will have leakage on the SAP vacuum control solenoid at the air vent, this is normal.

In the parts diagram below, item #3 which is the harder plastic vacuum line that runs along the valve cover gets extremely brittle and breaks easily, many times on the bottom where it is not visible. Many people just replace item #3 & both sort sections of item #4 with a single piece of vacuum hose from the SAP air valve to the extremely difficult connection to reach under the intake manifold. Also note there are a few additional short sections of rubber vacuum line that can also cause you problems under the intake, items #7 & #9.

Other areas to look at include:
Intake manifold gasket, this can leak to single cylinder, cold start misfires that usually only happen after sitting overnight and at temps below 50F. These are almost impossible to test for with smoke and/or spraying with brake cleaner or carb cleaner.
CCV overall, but the oil drain back hose is the most common failure point.
Fuel Pressure Regulator vacuum hoses - http://forum.e46fanatics.com/showpos...1&postcount=30
Plastic check "T" fittings and associated rubber vacuum hoses and rubber caps - http://forum.e46fanatics.com/showthr...500&highlight=IAT (Intake Air Temperature) sensor O-ring leakage, O-ring is cheap and easy replace. BMW Part #13621743299 Note the IAT is located between intake runner #3 & #4 under the main engine cover.
ICV and its L shaped hose that connect near the throttle body.
Throttle body O-ring.
Upper intake flexible boot from MAF to coupler.
Power brake booster vacuum hose.
Air pump check valve vacuum hose.
Idle control valve and associated hoses.
Dip stick O-ring(s).
Fuel injector O-rings.
Oil fill cap.
Valve cover gaskets and small top seals.
Air distribution manifold and O-rings, over top of the intake manifold with a connection to each intake with an O-ring.
Fuel pressure regulator vacuum hoses.
EVAP hoses and valve.
VANOS seals, usually cause more MPG loss and upper RPM loss of performance, however, many have claimed that VANOS seals have help these issues.

Almost all of intake air leaks can cause misfire codes, O2 sensor codes, fuel trim codes, rough running and stalling. All these parts are basically rubber and after 7+ years and are starting to fail because they are subjected to high heat, gas and oil vapors, thermal cycling and vibration and it is time that they be replaced.

Lately there have been a lot of owners that have been dealing with what appears to be single cylinder, cold start misfires that cannot or do not appear to be corrected by eliminating vacuum leaks and they are being given advice to open the engine and replace lifters or take other drastic measures. There seems to be a lot of consensus that there is no way a vacuum leak can cause a single cylinder misfire. I say there clearly are certain vacuum leaks that will cause single cylinder misfires and it is my position that I would invest the time, money and effort to replacing hoses, seals and gaskets long before I would be taking the engine apart. You do have to use some logic on your approach and make decisions along the that that maybe you will pull injectors and have them professionally cleaned by someone like www.witchhunter.com before you possibly may pull your intake and/or tear into the motor. Also you may want to make sure you have performed a cylinder leakage and compression test long before removing the intake as well. Also do not forget to actually make sure the connector to the problem cylinder injector and ignition coil are tight, you may want to take a sharp pick and actually try to tighten the terminal inside the connectors for the injector and coil.

There has been some discussion that hydraulic lifter bleed down may be the cause of single cylinder, cold start misfires. This may be the case and a few owners have had lifters replaced, however, it is really hard to tell if the lifter was really the problem, or if when replacing the lifter a leaking valve cover gasket and/or other hose or gasket may have also been replaced during the repair that may have really been the source of the problem?? If it was my car, the LAST thing I would even consider would be to tear into the engine unless I had a really good idea that I had ruled out all the basic maintenance issues and common problems these car tend to have as they aged. Again, I would be focused on eliminating possible burnt valves early on in the process with cylinder leakage and compression testing, then methodically address the move obvious problems as I did things like professional injector cleaning and determining if intake manifold gaskets should be replaced.

Something to also keep in mind, if you are totally unsuccessful in isolating a persistent misfire problem, please keep in mind you may in fact have an engine mechanical problem. Although rather rare, there have been a number of higher mileage cars that have been found to have a burnt exhaust valve in one cylinder. If this is the case the repair cost, required skill, time and effort is greatly increased.

Following are some recently examples of burnt exhaust valve that caused persistent misfire problems both cold and hot:

I had a car the other day with over 12 CEL/MIL trouble codes that included misfires on individual cylinders, misfires on multiple cylinders, O2 sensor out of range, O2 sensor codes, fuel trim codes.

Turns out the primary problem was the $11 CCV oil return hose between the CCV and the dip stick tube, also the DISA O-ring was rather loose. $25 later no CEL/MIL, no trouble codes, no misfires or rough running.

Quick suggestion, if you car is running poorly now that the weather is cold, replace at least the lower intake elbow, the DISA O-ring and the CCV lower oil return hose, clear the DME codes, about $50. Then worry about other things if the car is still running poorly or has additional CEL/MIL codes.

NOTE: Many times the Mass Air Flow sensor will soft fail or degrade over time and cause an under reported airflow amount, which in turn may cause the long term fuel trims to increase above the 10% mark. An indicator of a degraded or soft failed MAF may be that the short term fuel trim is within +/- 3% or less at idle, but your long term fuel trims are much further off. Additionally a degraded or soft failed MAF may cause the CEL to come on only on the highway and not around town. Vacuum/air leaks are more likely to trigger a CEL during idle and round town, where a degraded or soft fail MAF is more likely to trigger while on the highway.

Before proceeding with parts purchases, I have made every attempt to present accurate information here, however, it is your responsibility to verify part numbers @ www.realoem.com or other BMW parts guide to verify proper part application for your vehicle!

Footnote/disclaimer on this thread, sorry if it seems some of my writing is a bit disjointed. This originally started out as a very simple 1-2 paragraph look what problem I had and how I resolved the issue. But then the thread this took on a life of it own. Many, many additions and edits and although I am not very proud of what I have put together, it will hopefully help some of you out with your problems. If I had enough time, I should really sit down and rewrite this information from the ground up so it is a bit more cohesive and clear, but I think overall most of you can see beyond my ramblings and will get the point. I do from time to time make corrections and additions as needed and as long as this thread has the edit feature still active, I may make slight corrections and additions from time to time. I hope this has helped some BMW owners out with identifying and correcting their issues and allow you to keep you car reliable.

Special thanks for the many other Fanatics that have allowed me to use some of their photos to illustrate this thread and help out the community! Also this information is a work in progress, if there are any mistakes, errors or omissions, please PM me with specific details, corrections and comments

The only problem with your post is that the fix for the CEL/MIL depends on the code that accompanies the light. Many of the things you talk about are for the remedy of a lean condition, and there are two codes that come up for that, P0171 and P0174.

These are two codes out of several hundred. So, the best advice when the Check Engine Light comes on is to pull codes and go from there. It is almost always a bad idea to blindly aim your shotgun under the hood and start wrenching on whatever you hit.

Agree that you should get codes read and make educated decisions, however, these problems cause more that just the 2 lean codes you listed.

But also from looking at a lot of these cars lately, all e46 are of the age and mileage the the 3 items I listed are VERY common, easy to inspected for and cheap and easy to replace. A few screw drivers and a small socket set is all that is needed to DIY the items I have listed.

This is not like dealing with VANOS O-rings or complete CCV replacement.

Just wanted to put out there the simple and common causes before tackeling the harder and more expensive issues. The assumption is also basic maintenance has been kept up like spark plugs, fuel filter, air filter and so on.

So I took my car to an Indy shop and they said my MAF needed replacement due to all cylinder misfires and stalling. I just picked up a used BMW MAF with matching part #, but it seems the problem is worse. My old MAF responds to the throttle during start up and I can actually drive the car after warm up, but the new one cannot idle at all and it just stalls. It will start up and idle for a second before it just drop. Can someone give me an idea of what will cause the new MAF to do that and not on my old MAF?

Get the trouble codes read and focus at least on the lower CCV oil drain hose and the DISA O-ring.

I expect even if your lower intake elbow is not cracked, it could use a replacement if it is original anyway. You will just eliminate a future problem.

You should get your codes read as it will help start to identify what problems are likely to be happening. And what if any you are correcting. Start a log, write the date and mileage down each time you read the codes, then clear them. This is the only way to track where things are headed with each problem correctly. To many focus on component replacement before eliminating the obvious problems with the cheaper rubber, plastic and O-rings that have all aged and are going to be problems anyway.

Yes there are other issues that can cause your problems, but if you follow my directions, I would be surprised if you do not have problems with at least 2 out of the first 3 things I have listed.

Air/vacuum leaks are a major issue with engine controls on this engine and there are many places they can happen. Almost all of them are rubber or plastic that have gotten old, hard and cracked.

I have been having some seriouse issue with cold weather start up lately. when I start the car it will start right up but then idles real rough for about 2 min untill the car warms up. The idle dips and and rises and but then becomes stable once the car warms up. I have replaced the CCV as well as the upper and lower intake boot both of which had tears in them but the problem still persists after startup. I also cleaned the ICV and Throttle Body when I did the CCV, once the car is warm however it runs fine. I have the new O-Ring for the DISA that I have to replace and then maybe the hose from the air pump to the air pump check vavle. Hoepfully this solves my problem and I will repost back but I am also going to check that hose on the air pump to see if that is really causing all my issues since i havent purchased that part yet. Since it is on the top of the emgine I can remove and inspect it.

Simple test for the SAP check valve vacuum hose is to disconnect the small vacuum hose at the SAP check valve and either blow into the hose (you may need another length of hose and a nipple) and/or connect a hand vacuum pump up to the vacuum hose that connects to the SAP check valve.

You should not be able to blow/move air in this section and/or it should hold a vacuum. This hose has and electric check valve at the other end near the throttle body.

If you can blow/move air or this line does not hold a vacuum, it has a leak. Most likely the hard plastic pipe around the valve cover is broken on the bottom where you cannot see it?

Note this line only has vacuum applied for the first 90 seconds on cold start up. So if you car runs fine from 90-120 seconds and beyond, I would think this is a likely source of your problem.

2004, lower CCV lower oil drain hose was not rotted yet, however, very soft and on the way out, hose replaced.

DISA seal were in ok shape, could have used the O-ring, however, the DISA flap was spinning on shaft, pin probably broke, dropped out? New DISA ordered.

Original intake boots on the car, will be replacing them as a preventative measure as they are getting old and hard.

What I did find is whomever last worked on the car did not tighten up the upper intake hose to the MAF and the hose was about half way off the MAF.

So the basic problem was the upper intake boot was loose on the MAF and the car has a bad DISA.

This has been causing rough running when cold and codes to trigger. Simple problem, but the owner wants to keep the car at least 2+ more years and plans on keeping it reliable so the DISA, and intake boots will be replaced.